Endoscope apparatus

ABSTRACT

An endoscope apparatus having an insertion part which includes an object optical system in order to conduct measurements or stereoscopic-vision observations, using the object optical system with a moderate parallax, a moderate size of an image can be provided without making an endoscope thick in diameter.

This Appl. is a Div. of Ser. No. 09/714,489 Nov. 17, 2000 now U.S. Pat.No. 6,632,172.

FIELD OF THE INVENTION

This invention relates to an endoscope apparatus with an insertion parthaving a small outer diameter which includes an object optical system toconduct measurements or stereoscopic-vision observations.

BACKGROUND OF THE INVENTION

Conventionally, an endoscope which includes a long and thin insertionpart which is inserted into a cavity or the intra-corporeal of a humanbeing for observation, etc., has been widely used in both the industrialfield and the medical field. Furthermore in recent years, there havebeen a great need to measure the size and the depth of flaws and cracksin the industrial field, and to perform surgery using an endoscope inthe medical field. Moreover in the medical field, using stereo images torecognize depth information is well known.

A conventional endoscope in which stereo observation are possible isdescribed in Japanese Laid-open Patent Publication No. 8-29701. As shownin FIG. 6, two objective-lens systems are arranged in parallel and atthe end of an endoscope insertion part. The endoscope conducts parallaxstereoscopic vision by receiving an image from two image-pick-up devices(henceforth, CCD) and shifting the image due to the positionaldifferences of the two CCDs.

In the optical system with two CCDs, since the number of pixels can beincreased as compared to one CCD, it is effective in improving the imagequality of stereo images and the precision of measurements. However, byarranging two CCDs in parallel, it then becomes difficult to reduce thesize of an endoscope which makes it difficult to observe a narrow siteor perform minimum invasive surgery.

A conventional endoscope having an optical system in which an image witha parallax is formed on one CCD is described in Japanese Laid-openPatent Publication No. 7-35989. As shown in FIG. 7, this optical systemhas one CCD on the extension line of the respective optical axis of thetwo object optical systems arranged in parallel to form two images. Thedistance between the two optical axes is hereinafter referred to as “theoptic-axial distance”.

On the one hand, in recent years the trend has been toward smaller-sizedCCDs. However, if the optimum optic-axial distance is determined suchthat a part of the object optical system nearest to the object has amoderate parallax, and an image is formed on the CCD with thatoptic-axial distance, as shown in FIG. 8, the center of an image will bepositioned at the end of the CCD, if the CCD is small. That is, the areaof the images at the right and left sides of the CCD, marked withdiagonal lines in FIG. 8, decreases and causes interference with thestereoscopic vision and measurements.

Conversely, if the size of the CCD to be used is determined inaccordance with the size of an endoscope, and the distance between thecenters of the optimum images on the CCD is also determined, as shown inFIG. 9, there is a possibility that a parallax required for ameasurement or for stereoscopic vision cannot be obtained if theoptic-axial distance is equal to the distance between the centers of theimages on the CCD for the nearest object to the object optical system.

Therefore, in order to obtain a moderate parallax required for ameasurement or a stereoscopic vision as well as an acceptable image onthe CCD, the optic-axial distance of an object optical system, and thedistance between the centers of the images on CCD need to be varied.

However, the optic-axial distance of an object optical system influencesa parallax which is important at the time of a stereoscopic-visionobservation and the precision at the time of measurement. If theoptic-axial distance of the object optical system nearest to the objectis narrow, a parallax will decrease so that depth information becomeshard to obtain when carrying out a stereoscopic vision and a measurementerror becomes large when carrying out a measurement operation.

Conversely, if the optic-axial distance of the object optical systemnearest to the object is wide, a parallax will become large. Althoughthe precision of a measurement improves, the problem will arise that theend of an endoscope becomes large. And since a parallax is too largewhen carrying out a stereoscopic-vision observation, it is hard toobserve on the contrary.

A parallax depends not only on the optic-axial distance of the objectoptical system nearest to the object but also on the distance to theobject to be observed. In other words, the closer the object is, thelarger the parallax becomes, and the farther it is, the smaller theparallax becomes.

Based on the above, in order to obtain a moderate parallax required formeasurement and for a stereoscopic-vision observation depending on theobservation distance, and in order not to make the size of an endoscopelarge, the optic-axial distance of the object optical system at a partthereof nearest to the object should be determined.

A conventional example in which the optic-axial distance of an objectoptical system is different from the distance between the centers of theimages on the CCD is described in the Japanese Laid-open PatentPublication No. 62-215221.

In this example, as shown in FIG. 10, by sandwiching a parallel flatdioptric element with a pair of optical systems, the optic-axialdistance of an object optical system is narrowed towards the center ofthe image on the CCD. In such an optical system, if the CCD is small,the parallel flat dioptric element must be small. However, it isdifficult to design and manufacture a small parallel flat dioptricelement, and still more difficult to sandwich it with a pair of opticalsystem.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an object opticalsystem with a moderate parallax and a moderate image size, withoutmaking the insertion part of the endoscope thick in diameter.

In an endoscope apparatus, according to the present invention, equippedwith an object optical system to conduct a measurement or astereoscopic-vision observation, as shown in FIG. 1, the object opticalsystem comprises a pair of negative lenses; a first pair ofpositive-lenses; a brightness diaphragm; a second pair ofpositive-lenses; and an image-pick-up device for forming an objectimage. These elements are arranged in order from an object side. A pairof optical axes are defined by the pair of negative lenses, the firstpair of positive-lenses and the brightness diaphragm. Centers of thesecond pair of positive-lenses are arranged eccentrically with respectto the pair of optical axes in a direction towards each other's center.

The lenses means can be defined as a single-lens, plural single-lenses,or cemented lens or combination thereof.

The eccentric lenses may be provided on only one side of the second pairof positive-lenses, or on a part of the second pair of positive-lenses.It is noted that the centers, of the positive-lenses of the second pair,is the center of the circle if the lens shape is a circle, and it is thecenter of gravity of a polygon if the lens shape is a polygon.

The endoscope apparatus according to this invention, wherein thefollowing conditional expression is satisfied:0.2≦x/d≦0.9  (1)

wherein x represents an optic-axial distance of said pair of opticalaxes on the image side, and d represents the optic-axial distance ofsaid pair of optical axes on the object side.

The centers of the positive-lens of the second pair are arrangedeccentrically with respect to a pair of optical axes in a direction inwhich the centers come closer to each other symmetrically and by thesame amount. According to this invention, the second pair ofpositive-lenses on the image-pick-up device side from a brightnessdiaphragm is arranged to be inwardly eccentric, with respect to eachoptical axis on the object side from a brightness diaphragm, towards thehorizontal direction of the screen.

The amount of the eccentricity of the second pair of positive-lensesdoes not necessarily need to be symmetrical. In a stereoscopic-visionendoscope, however, it is important to minimize the aberrational shiftof the left and right images. It is preferable that the left and rightimages are balanced by making the eccentricity symmetric.

Moreover, each of the positive-lenses of the second pair has a cutoutportion at the peripheral thereof where the two lenses abut so that thecenters of the positive-lenses come closer to each other. Specifically,the distance between the centers of circumferences of thepositive-lenses is less than the sum of radii of thereof. It ispreferable that the shape of the cutout portion be a straight line whichis easy to process.

The centers of the positive-lenses of the second pair are arranged totilt eccentrically with respect to a pair of optical axes in a directionin which the centers come closer to each other symmetrically and by thesame amount.

The amount of the eccentricity of the second pair of positive-lensesdoes not necessarily need to be symmetrical. In a stereoscopic-visionendoscope, however, it is important to minimize the aberrational shiftof the left and right images. It is preferable that the left and rightimages are balanced by making the eccentricity symmetric.

Moreover, each of the positive-lenses of the second pair has a cutoutportion at the peripheral thereof where the two lenses abut so that thecenters of the positive-lenses come closer to each other. Specifically,the distance between the centers of circumferences of thepositive-lenses is less than the sum of radii of thereof. It ispreferable that the shape of the cutout portion be a straight line whichis easy to process.

According to this invention, it is constituted so that the followingconditional-expression (2) may be satisfied:0.03L<d<2L  (2)

wherein d represents the optic-axial distance of said pair of opticalaxes at the object side, and L represents the best observation distanceof said object optical system.

The minimum of this equation is necessary a condition in order to obtaina parallax and furthermore to obtain precision required at the time ofmeasurement. As illustrated in FIG. 1, when setting the best observationdistance at L, it is considered that 1 degree or more is required for anintrovert angle (θ). The best observation distance herein implies adistance to the object which is most suitable for the observation. Inthe case of an endoscope, it is usually about 5-100 mm. If the introvertangle (θ) is 1 degree or less, a parallax will decrease and it becomeshard to obtain information on the depth direction when carrying out thestereoscopic vision. Moreover, in that case, a measurement error becomeslarge when measuring an objective shape.

The value of the upper limit of the above formula (2) not only restrainsthe size of an end portion of the endoscope from becoming large, butalso prevents the observation from becoming difficult to observe becauseof a too large parallax.

According to this invention, the endoscope apparatus is detachable fromthe image-pick-up device.

As illustrated in FIG. 1, an end adapter system is detachable in thedirection of an arrow at the chain-line position. The rear part is theendoscope side part containing a cover glass 7 and an image-pick-updevice 8. Accordingly, the angle of view of the endoscope, the viewingangle, and the introvert angle which influences a parallax arearbitrarily exchangeable by replacing the adapter part.

According to this invention, a prism for converting the line of sight isarranged between an object and the pair of negative lenses. As viewedfrom the side in FIG. 3, at least one prism for converting the line ofsight 10, a pair of negative lenses 1, a first pair of positive-lenses2, a brightness diaphragm 3, the second pair of positive-lenses 4, andan image-pick-up device 8 are provided in order from the object side.The second pair of positive-lenses are eccentric with respect to each ofthe optical axis on the object side from the brightness diaphragm. Withthis structure, the angle of view is determined by the pair of negativelenses and the first pair of positive-lenses on the object side from thebrightness diaphragm. Simultaneously, aberrations, such as aspherical-aberration and curvature of field, are restrained as well.And, by shifting the optical axes of the second pair of positive-lensesafter extracting a luminous flux through the brightness diaphragm, theaberrational influence by eccentricity is decreased. Free selection ofthe line of sight is effective in observing a narrow space.

According to an embodiment of this invention, an effective image-pick-uprange of the image-pick-up device is 2 to 2.5 mm or less.

In the object optical system of the endoscope according to the presentinvention, as shown in FIG. 5, the object optical system comprises abrightness diaphragm 3, a pair of positive-lenses 11, 12 and animage-pick-up device 8 for forming an object image. These elements arearranged in order from the object side. An optic-axially eccentricdevice 13 is arranged adjacent the brightness diaphragm 3, and theoptic-axial distance on the object side determined by the optic-axiallyeccentric device 13 is eccentric with respect to the optic-axialdistance determined by a pair of positive-lenses 11, 12 on the imageside from the brightness diaphragm.

Moreover, according to this invention, the followingconditional-expression (1) is satisfied:0.2≦x/d≦0.9  (1)

wherein x represents an optic-axial distance of a pair of optical axeson the side of the image-pick-up device from the brightness diaphragm,and d represents the optic-axial distance of the pair of optical axes onthe side of an object from the brightness diaphragm.

The optic-axially eccentric device is disposed within 0.5 mm from thebrightness diaphragm. The reason why the optic-axially device isprovided adjacent to the brightness diaphragm is that the size of theoptic-axially device becomes small if the amount of eccentricity becomescomparatively small when using a small-sized image-pick-up device.Therefore, it is desirable to arrange it adjacent the to brightnessdiaphragm with a low light height.

The term “adjacent the brightness diaphragm” herein implies not onlythat the optic-axially eccentric device is disposed within 0.5 mm fromthe brightness diaphragm, but also that the brightness diaphragm can bedisposed within the optic-axially eccentric device. In this embodiment,it is preferable that the small image-pick-up device have an effectiveimage-pick-up range of 2 to 2.5 mm or less.

Moreover, the optic-axially eccentric device is provided on only onepair of the pair of positive-lenses. In this constitution, it is moredesirable to provide only one optical element on one of the opticalsystems which makes it eccentric to the optical axis of the otheroptical system in a horizontal direction of the screen. This is because,in the endoscope of a narrow diameter, if two optical elements whichmake the optical axes eccentric, like a prior art example, each opticalelement should be made small and a manufacturing process becomes muchmore difficult.

According to another embodiment, the optic-axially eccentric device hasa prism with two reflecting surfaces, or two reflective mirrors.

According to this invention, the following conditional expression issatisfied:0.03L<d<2L  (2)

wherein d represents the optic-axial distance of a pair of optical axeson the object side from said brightness diaphragm, and L represents thebest observation distance of the object optical system.

Preferably, the apparatus is detachable from the image-pick-up device.Preferably, the effective image-pick-up range of the image-pick-updevice is 2 to 2.5 mm or less.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an object optical system according to a first exampleof the present invention.

FIG. 2 illustrates a sectional drawing including the frame of an adapterpart shown in FIG. 1.

FIG. 3(a) illustrates an object optical system according to a secondexample of the present invention.

FIG. 3(b) illustrates a side view of the object optical system shown inFIG. 3(a).

FIG. 4 illustrates an object optical system according to a third exampleof the present invention.

FIG. 5 illustrates an object optical system according to a fourthexample of the present invention.

FIG. 6 illustrates a conventional object optical system of an endoscopewhich enables stereoscopic vision.

FIG. 7 illustrates a second conventional object optical system of anendoscope which enables stereoscopic vision.

FIG. 8 illustrates that the center of an image will be positioned at theend of the CCD, if the CCD is small for the second conventional systemshown in FIG. 7.

FIG. 9 illustrates a possibility that a parallax required for ameasurement or for stereoscopic vision cannot be obtained for the secondconventional system shown in FIG. 7.

FIG. 10 illustrates a third conventional system that sandwiches aparallel flat dioptric element with a pair of optical systems.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the accompanying drawings, examples of object opticalsystems illustrating the embodiments of the present invention, will bedescribed hereinafter.

In the following examples, same elements of the object optical systemsare identified by the same reference numerals.

FIG. 1 illustrates an object optical system according to a first exampleof the present invention. In this example, the object optical systemincludes a pair of negative lenses 1, a first pair of positive-lenses 2,a brightness diaphragm 3, a second pair of positive-lenses 4, infraredcut off filter 5, cover glasses 6, 7, an image-pick-up device 8, inorder from an object side.

The second pair of positive-lenses 4 are eccentric to the respectiveoptical axis from the object side to the brightness diaphragm 3. Inaddition, a pair of negative lenses 1 are plane-concave lens with theconcave surface oriented to the image-surface side. A first pair ofpositive-lenses 2, behind the negative lens 1, consists of aconcave-convex doublet.

The brightness diaphragm 3 consists of two apertures. Moreover, thesecond pair of positive-lenses 4 consist of respective plane-convex lenswhich are eccentric to each optical axis on the object side, from thebrightness diaphragm 3, in the screen horizontal direction, eccentric byin the same amount, respectively, and the convex surface are oriented tothe object side. The center part shown by symbol A is cut out so thateach lens does not interfere with the other.

The infrared cut off filter 5 in common in the left and right opticalsystems, the cover glass 6, 7 and the image-pick-up device 8 arearranged behind the lens. This Example has the structure of an endadapter system detachable in the direction of an arrow at the chain-lineposition.

The rear part of the endoscope includes a cover glass 7 and animage-pick-up device 8. Accordingly, it is possible to changearbitrarily the angle of view of the viewing angle of an endoscope, andthe introvert angle which influences a parallax by replacing an adapterpart.

The value corresponding to each above-mentioned conditional expressionand lens data are as follows.

x = 0.986 d = 1.599 L = 13.69 0.2 ≦ x/d = 0.62 ≦ 0.9 0.03 L < d = 0.12 L< 2 L Object distance 13.6896 r1 = infinity d1 = 0.04381 n1 = 1.88300 ν1= 40.78 r2 = 0.8436 d2 = 0.2409 r3 = infinity d3 = 0.4275 r4 = 1.9713 d4= 0.6727 n4 = 1.84666 ν4 = 23.78 r5 = 0.9857 d5 = 1.3142 n5 = 1.51633 ν5= 64.14 r6 = −1.3015 d6 = 0.7051 r7 = infinity d7 = 0.1095 (diaphragm)r8 = 2.2431 d8 = 0.8785 n8 = 1.78800 ν8 = 47.37 r9 = infinity d9 =0.0329 r10 = infinity d10 = 1.3142 n10 = 1.51400 ν10 = 75.00 r11 =infinity d11 = 0.0329 r12 = infinity d12 = 0.4381 n12 = 1.88300 ν12 =40.76 r13 = infinity d13 = 0.2190 r14 = infinity d14 = 0.8761 n14 =1.88300 ν14 = 40.76 r15 = infinity d15 = 0.3286 n15 = 1.49700 ν15 =81.61 r16 = infinity d16 = 0.0329 r17 = infinity The eccentricity ofeach convex lens 4 = 0.3356 horizontally.

FIG. 2 is a sectional drawing including the frame of an adapter part.The structure is watertight by incorporating a cover glass 9 at its end.

FIGS. 3(a) (b) illustrate an object optical system according to a secondexample of the present invention. FIG. 3(a) is a top view of the objectoptical system. FIG. 3(b) is a side view of the object optical system.In this example, the object optical system is different from the objectoptical system of the first example in that a cover glass 9 and a prism10 are arranged at the object side for converting a line of sight.

Namely, in order from an object side, the object optical systemsconsists of a prism 10 for converting the line of sight, a pair ofnegative lenses 1, a pair of positive-lenses 2, a brightness diaphragm 3consists of two apertures, a pair of second positive-lenses 4, aninfrared cut off filter 5, cover glasses 6, 7 and an image-pick-updevice 8.

At the end of the prism for converting the line of sight 10, the coverglass 9 is bilaterally arranged. The prism 10 for converting the line ofsight also consists of a 90 degree side vision rectangular prism.

This example also has the structure of an end adapter system, whereinthe optical object system is detachable from the image-pick-up device 8.

Since the part at the side of the image-pick-up device 8 is common tothe optical object system of the first example, direct vision and sidevision can be obtained by replacing the adapter of the second examplewith that of the first example.

The value corresponding to each above-mentioned conditional expressionand lens data are as follows.

x = 0.856 d = 1.635 L = 10.167 0.2 ≦ x/d = 0.52 ≦ 0.9 0.03 L < d = 0.16L < 2 L Object distance 10.1672 r1 = infinity d1 = 0.3804 n1 = 1.88300ν1 = 40.76 r2 = infinity d2 = 0.1902 r3 = infinity d3 = 2.2580 n3 =1.88300 ν3 = 40.76 r4 = infinity d4 = 0.1303 r5 = infinity d5 = 0.3804n5 = 1.88300 ν5 = 40.78 r6 = 0.8526 d6 = 0.2092 r7 = infinity d7 =0.3215 r8 = 1.7120 d8 = 0.4990 n8 = 1.84666 ν8 = 23.78 r9 = 0.8560 d9 =1.1413 n9 = 1.51633 ν9 = 64.14 r10 = −1.1315 d10 = 0.7160 r11 = infinityd11 = 0.0951 (diaphragm) r12 = 2.0201 d12 = 0.7630 n12 = 1.78800 ν12 =47.37 r13 = infinity d13 = 0.0285 r14 = infinity d14 = 1.1413 n14 =1.51400 ν14 = 75.00 r15 = infinity d15 = 0.0285 r16 = infinity d16 =0.3804 n16 = 1.88300 ν16 = 40.76 r17 = infinity d17 = 0.1902 r18 =infinity d18 = 0.7609 n18 = 1.88300 ν18 = 40.76 r19 = infinity d19 =0.2853 n19 = 1.49700 ν19 = 81.61 r20 = infinity d20 = 0.0285 r21 =infinity The eccentricity of each convex lens 4 = 0.39 horizontally.

FIG. 4 illustrates an object optical system according to a third exampleof the present invention. In this example, the object optical system isdifferent from the object optical system of the first example in thatthe optic-axial distance of the optical axes is constant before andafter the pair of positive-lenses 4, and is narrowed by the convexsurfaces, oriented toward the object side, of the pair ofpositive-lenses 4.

The object optical system consists of a pair of negative lenses 1, apair of positive-lenses 2, a brightness diaphragm 3, a second pair ofpositive-lenses 4, an infrared cut off filter 5, and cover glasses 6, 7,an image-pick-up device 8 in order from an object side.

The positive-lenses 4 include a pair of positive lenses which areeccentric to each optical axis from the object side to by the brightnessdiaphragm 3, respectively.

This example also has the structure of an end adapter system, whereinthe optical object system is detachable from the image-pick-up device 8.

The value corresponding to each above-mentioned conditional expressionand lens data are as follows.

x = 0.77 d = 1.44 L = 12.512 0.2 ≦ x/d = 0.53 ≦ 0.9 0.03 L < d = 0.12 L< 2 L Object distance 12.512 r1 = infinity d1 = 0.40004 n1 = 1.883 ν1 =40.78 r2 = 1.1009 d2 = 0.2991 r3 = infinity d3 = 0.4004 n2 = 1.883 ν2 =40.78 r4 = 1.2396 d4 = 0.3815 r5 = 1.4434 d5 = 1.091 n5 = 1.84666 ν5 =23.78 r6 = 0.7628 d6 = 0.9842 n6 = 1.51633 ν6 = 64.14 r7 = −1.1285 d7 =0.05 r8 = infinity d8 = 0.1001 (diaphragm) r9 = 1.5541 d9 = 0.933 n9 =1.788 ν9 = 47.37 r10 = 2.7305 d10 = 0.4665 n10 = 1.51633 ν10 = 64.14 n11= 2.5486 d11 = 0.3003 n12 = infinity d12 = 1.2012 n12 = 1.514 ν12 =75.00 n13 = infinity d13 = 0.03 n14 = infinity d14 = 0.4004 n14 = 1.883ν14 = 40.76 n15 = infinity d15 = 0.2002 r16 = infinity d16 = 0.8008 n16= 1.883 ν16 = 40.76 r17 = infinity d17 = 0.3003 n17 = 1.497 ν17 = 81.61r18 = infinity d18 = 0.03 r19 = infinity The eccentricity of each convexlens 4 (Angle α of FIG. 4) = 10 degrees

FIG. 5 illustrates an object optical system according to a fourthexample of the present invention. In this example, the brightnessdiaphragm 3 consists of two apertures.

Further, the optical object system includes a pair of positive-lensesconsisting of a pair of convex meniscus lenses 11 with the concavesurface oriented toward the image side, a pair of positive lenses 12with the convex surface oriented to the object side, an infrared cut offfilter 6, and cover glasses 6, 7, in order from the brightness diaphragm3.

Moreover, a parallelogram prism 13 which makes the optical axis behindthe brightness diaphragm 3 eccentric is arranged in only one opticalsystem on an object side from the brightness diaphragm 3. Furthermore,in the other optical object system only the parallel plate 14 isarranged so that optical axis is not eccentric behind the brightnessdiaphragm 3. This is in contrast to the conventional optical system, forexample, as shown in FIG. 10, wherein a pair of prism are arranged.

However, the parallelogram prism 13 which makes the optical axiseccentric has a comparatively small eccentricity so a precise prismprocess in not necessary.

Moreover, although a prism element was used in this example, similareccentricity may be obtained by arranging the two mirrors facing to eachother.

This example also has the structure of an end adapter system, whereinthe optical object system is detachable from the image-pick-up device 8.

The value corresponding to each above-mentioned conditional expressionand lens data are as follows.

x = 0.833 d = 1.351 L = 10.094 0.2 ≦ x/d = 0.62 ≦ 0.9 0.03 L < d = 0.13L < 2 L Object distance 10.0937 r1 = infinity d1 = 1.0372 n1 = 1.88300ν1 = 40.76 r2 = infinity d2 = 0.0926 (diaphragm) r3 = −0.6631 d3 =0.9568 n3 = 1.88300 ν3 = 40.76 r4 = −0.8176 d4 = 0.0926 r5 = 1.6107 d5 =0.9260 n5 = 1.51400 ν5 = 75.00 r6 = infinity d6 = 0.3704 n6 = 1.88300 ν6= 40.76 r7 = infinity d7 = 0.1852 r8 = infinity d8 = 0.7408 n8 = 1.88300ν8 = 40.76 r9 = infinity d9 = 0.4630 r10 = infinity d10 = 0.0278 n10 =1.49700 ν10 = 81.54 r11 = infinity d11 = 0.0037 r12 = infinity Theeccentricity in the parallelogram prism 13 = 0.518 horizontally.

In addition, in each Example, x, d, L, and lens data are standardizedbased on the focal-length f=1. Moreover, r1, r2, . . . express theradius of curvature of each lens surface, cover-glass surface, or prismsurface; d1, d2, . . . express the thickness or the air space of eachlens, cover glass, or prism; n1, n2, . . . express the refractiveindexes of each lens, cover glass, or prism; and v1, v2, . . . expressthe Abbe number of each lens, cover glass, or prism, respectively.

1. An endoscope apparatus equipped with an object optical system toconduct measurements or stereoscopic-vision observations, said objectoptical system comprising: a brightness diaphragm; a pair ofpositive-lenses; and an image-pick-up device for forming an objectimage, said elements being arranged in order from an object side whereinan optic-axially eccentric device is arranged adjacent said brightnessdiaphragm, and wherein the optic-axial distance on the object sidedetermined by said optic-axially eccentric device is eccentric withrespect to the optic-axial distance determined by a pair ofpositive-lenses on an image side from said brightness diaphragm.
 2. Theendoscope apparatus according to claim 1, wherein the followingconditional expression is satisfied:0.2≦x/d≦0.9 wherein x represents the optic-axial distance of a pair ofoptical axes at said image-pick-up device; and d represents theoptic-axial distance of a pair of optical axes on the object side fromsaid brightness diaphragm.
 3. The endoscope apparatus according to claim2, wherein said optic-axially eccentric device is disposed within 0.5 mmfrom said brightness diaphragm.
 4. The endoscope apparatus according toclaim 3, wherein said brightness diaphragm is disposed within saidoptic-axially eccentric device.
 5. The endoscope apparatus according toclaim 2, wherein said optic-axially eccentric device is provided on onlyone pair of said pair of positive-lenses.
 6. The endoscope apparatusaccording to claim 2, wherein said optic-axially eccentric device has aprism with two reflecting surfaces or two reflective mirrors.
 7. Theendoscope apparatus according to claim 1, wherein the followingconditional expression is satisfied:0.03L<d<2L  (2) wherein d represents the optic-axial distance of a pairof optical axes on the object side from said brightness diaphragm, and Lrepresents the best observation distance of said object optical system.8. The endoscope apparatus according to claim 1, wherein said apparatusis detachable from said image-pick-up device.
 9. The endoscope apparatusaccording to claim 1, wherein said effective image-pick-up range of saidimage-pick-up device is 2 to 2.5 mm or less.